CHICAGO (Reuters) - An experimental treatment in mice
showed promise in reversing a rare blood disease that can cause
leukemia, U.S. researchers said on Monday, offering a glimpse
of how the drug may work as it begins testing in humans.

In experiments at Harvard Medical School in Boston and the
University of California, San Diego, researchers found the
compound blocked a genetic mutation that causes three kinds of
leukemias.

The studies tested a compound supplied by privately held
biotechnology company TargeGen in San Francisco, which has just
begun early testing in humans.

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It targets a genetic mutation in the JAK2 gene that causes
most cases of the leukemias polycythemia vera, essential
thrombocytosis and primary myelofibrosis, which affect up to
100,000 people in the United States.

The mutation in the JAK2 gene causes an overproduction of
blood cells. The TargeGen compound TG101348 is designed to
block the JAK2 mutation that causes this.

The idea is to set errant cells back on the right path,
said Dr. Catriona Jamieson of the University of California, San
Diego, whose paper appears in the journal Cancer Cell.

"By using how stem cells work and how they can go awry, we
can redirect them using very targeted inhibitors that get these
cells back on track," Jamieson said in a telephone interview.

Her experiments showed the compound reversed the disease in
cell cultures. Her team also found the drug reversed disease in
mice that had an engineered version of the mutant gene and
those injected with stem cells from humans with the disorder
polycythemia vera.

In a separate study in the same journal, Dr. Gary Gilliland
and colleagues induced polycythemia in 168 mice. They gave high
and low doses of the compound TG101348 daily for seven weeks to
112 mice. All the mice that got the higher dose survived, six
in the placebo group died and one in the low dose group died.

"We saw that the compound alleviates and reverses the
symptoms in mice," said researcher Gerlinde Wernig, who worked
on the study.

"These are completely complimentary results," Jamieson said
of the two studies, which helped lay the foundation for the
human clinical trials which began last month.

Researchers at a half dozen prestigious medical centers
will participate in the human studies, which will test a small
dose of the drug in a few patients to see if it causes toxic
side effects.

"Our goal is to get an efficacious drug into use for
humans," said Gilliland, who is also a Howard Hughes Medical
Institute researcher.